I have been pondering lately about just how cool plants are -again! I've written about this in the past but was inspired to revisit the topic on this blog while listening to Glenn Keator, an engaging local author, educator, and plant enthusiast, discuss plant biology with the Marin Master Gardeners. It dawned on me how fortunate we are to be able to be so intertwined in the lives of so many plants and to be privy to the growing information regarding plants and plant lore. But it goes deeper than that. Our day to day relationships with plants as gardeners make us appreciate plants for the beauty they provide and we go about our roles of propagating, pampering, growing, and combining them in artistic and useful ways. But how often do we contemplate on how much we have in common and how much we owe it to plants for our very existence?
Vascular plants have been here on Earth, indeed, actually involved in the Earth’s evolution, for approximately 440 million years. There are approximately 350 thousand species of plants. We as gardeners know that many species are divided up into dozens of cultivars. The diversity is astounding. It’s cool to think that this many species have a whole energy system that is somewhat opposite that of ours: Plants use carbon dioxide to synthesize glucose and give off oxygen as a waste product. We use oxygen and glucose and give off carbon dioxide as a waste product. What goes around comes around.
Plants have evolved to accept light at two specific wavelengths. At these bluer and redder wavelengths, Chlorophyll molecules absorb light in the chloroplasts and we see them in the spectrum of what is not absorbed -green. Humans have been on the earth about 200 million years -less than half as long as plants. We are only now figuring out how to capture the energy of sunlight using photovoltaics. Thank goodness plants have been at it for such a long time. About 4.4 billion years ago our atmosphere was mostly carbon dioxide and water vapor -and almost no oxygen. Although the cyanobacteria started producing oxygen about 3.5 billion years ago, when the photosynthesizing plants evolved, the atmosphere changed dramatically and eventually the carbon dioxide got locked up in limestone, shells, and fossil fuels. This allowed oxygen breathing organisms to evolve. Now that we’ve been using those fossil fuels for a short while we’ve had to acknowledge the inconvenient truth that it creates more carbon dioxide in the atmosphere -and global warming. All the oxygen in the atmosphere also allows the creation of a layer of a special allotrope of oxygen that protects us from much of the suns ultraviolet radiation -the ozone layer. Also inconvenient is how our recent use of chlorofluorocarbons has reduced the number of these special types of oxygen and have allowed a growing amount of genetic damage to living organisms, including us. As I said, what goes around comes around.
The oxygen put into the atmosphere by plants also reacted with the ammonia from all the early volcanos and formed the nitrogen that now makes up 75% of our atmosphere and is the basic building block of all living tissues and amino acids. It’s the first number on any bag of fertilizer. What’s really amazing is that nitrogen can’t be used directly by plants or animals. Plants are part of a network though. Certain bacteria can use nitrogenase enzymes to “fix” ammonium into nitrites, which is then converted by other bacteria into nitrates, finally usable by plants to eventually form proteins, amino acids, and alkaloids. Some plants have even assimilated the useful nitrogen fixing bacteria into a symbiotic relationship in their roots as in the case with legumes, which makes up a large part of our diet. Most of our livestock feeds and pasture forage plants are legumes. Other plants do this too. I was surprised to find out that one of my favorite plants, Gunnera, also has a symbiotic relationship with a nitrogen fixing bacteria. So do Casuarinas, Myricas, and lichens. The real wonder of nitrogen, however, is when you put four of them in a ring, as in Chlorophyll.
Glenn brought up a fascinating bit of information to ponder: the similarities between chlorophyll and hemoglobin. In mammals hemoglobin makes up 97% of red blood cells (dry weight) and is the carrier of oxygen from lungs (or gills) to the rest of the body. It also is important in neurons and as an antioxidant in kidneys. In Hemoglobin, an iron ion is surrounded by four nitrogen in a plane, the iron being able to bind with oxygen and translocate it. In Chlorophyll, it's a magnesium ion that is similarly surrounded by four nitrogens. These amazing molecules are both produced through the same metabolic pathways and are called Porphyrins; coordinated with iron: you get the building blocks of our blood, coordinated with magnesium and you get the building blocks of our photosynthetic friends. Interestingly, but not surprisingly, very similar structures also create bacteriochlorophylls, other photosynthetic pigments that various bacteria use to absorb other wavelengths of sunlight -even sulfur based bacteria. These amazing similarities between the chemical workhorses of the biological world always inspires a sense of wonder in me, and at the same time a strong sense of oneness, -of connectedness; ourselves being so similar in basic structure to plants and even bacteria.
Just to leave Nitrogen as a basic building block really doesn’t tell the whole story, though: Nitrogen, along with a diverse group of bacteria and fungi, are also the basis for decomposition. Where do you think we’d be without decomposition? Talk about circular events. As gardeners we all know the wonders of compost. And what do we balance in the compost pile? Moisture, oxygen, nitrogenous material, and carbonaceous material. And where do you think the carbonaceous material came from? Plants, of course! The amazing evolutionary trick that plants pulled off was to develop cell walls. Animal cells only have a plasma membrane. Plants get a cell wall. By combining Hydrogen from water with Carbon from carbon dioxide, again using the amazing chlorophyll in photosynthesis, they can make carbohydrate frameworks: cellulose, by far the most abundant form of living terrestrial biomass. Plant cell walls consist of several layers of cellulose microfibrils held together with hydrogen bonds that allow high tensile strength and ... wood. Now where would us landscapers be without wood? Would our species have evolved at all?
So everything you breath, everything you eat, every hydrocarbon in your body -and every other body, big, small, human or otherwise- is the result of plants. We may think we are higher on the “food chain”, but perhaps we should think of it more like a tall pyramid with us precariously balanced at the top. The more solid foundation is made up of plants, bacteria, and minerals. The “carbon cycle” trumps the “food chain” any day anyhow, and it’s based on plants. When you think of all the bacteria and enzymes involved, then we’re looking at a Web. And when you sit out this summer warming yourself in the sun, or find yourself in the hot sun working in a garden, think about all the plants around you using that energy, turning those photons into sugars, breaking the chemical bonds of water, and be jealous. Be very jealous. I wish I could do that! Maybe I’d look good in green too. Now that we are “building green”, “voting green”, and “living green”, desperately trying to undue the mess our opposable thumbs and enlarged cerebral cortexes have gotten us into, it’s good to reflect on our fine photosynthetic friends and appreciate them not only for their beauty and usefulness, but for allowing us the ability to be here, use our senses, and appreciate anything in the first place. It sure is nice to know we are a part of the “green industry” and that our species has now acknowledged the Web and the importance of green. It's also really nice to know we're so closely related.
"All things share the same breath -the beast, the tree, the man... the air shares it's spirit with all the life it supports" -Chief Seattle
(chemical structures from Wikipedia- I love the Web!)
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